What utility or tool that runs which under Mac OS X 10.6 can I use to extract data (icon images and strings, etc.) from old Mac OS 7 (and earlier) resource files/resource forks? (...files created using ResEdit.)

There's also the system utilities DeRez/Rez (available in OSX 10.7 and some other versions) which allows for extraction of resource fork data into a form for use by the Rez resource compiler - e.g. extract icon data from an Icon file:

DeRez -only icns Icon^M > icon

It should be noted that the resulting files from both of the above commands require additional processing to convert the resources to a suitable form.